Periodic interrupter of direct current



P 3, 1940. F. SCHILGEN 2,213,553

PERIODIC INTERRUPTER 0F DIRECT CURRENT Filed NOV. 18, 1958 INVENTORFR/TZ SCZLGEN ATTORNEY Patented Sept. 3, 1940 UNITED STATES PATENTOFFICE PERIODIC INTERRUPTER OF DIRECT CURRENT Application November 18,1938, Serial No. 241,158 In Germany October 15, 1937 6 Claims.

In the operation of inverse rectiflers which are designed to interruptor chop a direct current by means of contacts at a rate of, say, 100 c.p. s., sparking is produced at the contacts and these 5 are liable tolead to permanent arcs especially where the potentials and the loads arehigh with the result that the contacts are destroyed.

To prevent sparking according to the invention, an auxiliary contact isconnected in parallel in relation to the periodically opened and closedmain contact and in series with an ohmic resistance, the said auxiliarycontact being subject to synchronous control in such a way that firstthe auxiliary contact is closed, then the main 15 contact, while firstthe main contact and then the auxiliary contact is opened.

The advantage residing in the invention flows from this consideration:The opening spark is due to the occurrence of a sudden rise of thepotential at the main contact at the instant the current is broken. Now,the said voltage leap is substantially lessened if part of the currentpreviously flowing has a chance to continue to flow by way of theauxiliary contact and the 25 ohmic resistance so that the occurrence ofan undue voltage leap is prevented. The closing spark similarly is dueto the fact that, in closed condition, the entire potential to behandled is active at the contact, and this voltage is then very abruptlyshort-circuited. But if, as here suggested, first the auxiliary contactis closed, the potential difference will first have a chance partiallyto equalize across the resistance in a somewhat gradual way so that whenthe surfaces 35 of the main contact come into physical touch, thereprevails no longer across them any unduly high potential. The auxiliarycontact itself will be called upon to carry no undue stresses or loadbecause of the fact that the ohmic resistance is connected in serieswith it.

Another advantage resides in the fact that the curve-shape of theinterrupted current will come more closely to the sine form because ofthe potential across the main contact being subject a to several risesand falls by stages; hence, the current will contain fewer harmonicsthan is true of a periodic direct current interrupter of theconventional type.

An exemplified embodiment of the invention is .9 shown in Fig. 1 asapplied to a pendulating or vibrating type of inverse rectifier thecircuit diagram of which is shown in Fig. 2. In the lower part of theclip-shaped member B is clamped unilaterally the leaf spring F so thatII it is capable of free oscillations. The upper,

.downwardly bent end of the clip supports the exciting coil S which byway of the exciting contact E at the spring periodically acts upon thekeeper A in such a way that the spring vibrates at its own naturalperiod. The spring F 5 supports on two outrigger springs FI and F2 asurface of the working contacts Kl, K2, respectively, the other surfacesbeing disposed on firmly secured counter-springs GI and G2. The spring Fmoreover carries upon each face a surface of two auxiliary contacts HI,H2, of which the re-- spective co-operating surfaces are attached to twofixed cooperating springs GI and G2. The intervening space of theworking surfaces of the auxiliary contacts HI and H2 is less than thedistance between those of the main contacts KI and K2 so that, when thespring vibrates, it is first the auxiliary contacts and then the maincontact that is closed, while the sequence in opening is reversed.

The fixed surfaces of the auxiliary contacts are connected with thefixed surfaces of the main contacts each by way of an ohmic resistanceRI and R2, respectively, of say 500 ohms each. The assumption is madethat the ohmic resistance of the primary of transformer T which, in theusual way, is connected with the chopper, is essen tially smaller andmay be equal to about 40 ohms, for instance. The source of directcurrent voltage Q of, say, 100 v. has its negative poles united with thecenter tap of the primary of the trans former, whereas the positive poleby way of the vibrating spring and one of the contacts Kl, K2, is nowconnected with one end, and now with the other end of the primary coilin alternate and periodic change.

In parallel relation to the primary coil of the transformer is a seriesarrangement of two condensers Cl, C2, the center tap of which is unitedby way of another ohmic resistance with the vibrating spring. The sizeof the said condensers in conjunction with the primary Winding of thetransformer and the resistances RI and R2 is decisive and governing forthe voltage change which occurs between contact-making at the maincontacts and that of the auxiliary contacts.

The entire device may be accommodated inside a bulb made of glass oriron which is free from oxygen and which, optionally, may instead befilled with nitrogen or hydrogen under a slight overpressure, so thatsparking will be still further suppressed.

I claim:

1. In a device of the kind described, a source of direct current, anarmature adapted to be vibrated between two extreme positions, atransformer having a primary winding and a secondary winding, aresistance and means cooperating with said armature for connecting saidsource of direct current across at least a portion ofsaid primarywinding through said resistance for an interval of time which commencesJust after the armature in moving toward one extreme position leaves apoint which is in the vicinity of the midpoint between said positionsuntil Just before it gets back to a point which is in said midpointvicinity and means cooperating with the armature for short-circuitingsaid resistance during an intermediate time interval of said first namedtime interval.

2. In a device for changing direct current into alternating current, atransformer having a primary winding and a secondary winding, avibrating armature and a driving means therefor, a pair of inputterminals across which is to be connected a source of direct current, aconnection between the armature and one of said terminals and meansconnecting the other input terminal to an intermediate point of saidprimary winding, a pair of contact points positioned with respect to thevibrating armature so that the armature contacts first one and then theother thereof in moving to one of its extreme positions, a second pairof contact points positioned with respect to the armature so that thearmature contacts first one and then the other thereof in moving to itsother extreme position, each of -the two contact points of said twopairswhich are contacted first by said armature being connected to theirrespective ends of the primary winding through a comparatively highresistance path, each of said other two contact points being connectedto their respective ends of the primary winding through a comparativelylow resistance path.

3. An arrangement as described in the next preceding claim characterizedby that in operation the armature breaks contact in moving from oneextreme position toward the other thereof first with the contact pointthat it was last to contact with in approaching that extreme position.

4. In a device of the kind described a transformer having a primarywinding and a secondary winding, a vibrator armature adapted to bevibrated between two extreme positions, a first pair of contact pointspositioned in the path of the vibrator armature so that the vibratorarmature contacts first one and then the other of said points in movingto one of its extreme positions, a second pair of contact pointspositioned in the path of said armature so that the vibrator armaturecontacts first one and then the other thereof in moving to the other ofits extreme positions, a

pair of input terminals across which is adapted to be connected a sourceof direct current, means connecting one of said input terminals to thearmature and the other thereof to an intermediate point of said primarywinding, a low impedance connection between one end of said. primarywinding and that one of said first pair of contact points which thearmature contacts last, a connection including resistance means betweenthe other of said first pair of contact points and said end of theprimary winding, 9. low impedance between the other end of the primarywinding and the contact point of the second pair of contact points whichthe armature contacts last and a connection including resistance meansbetween the other of said second pair of contact points and said lastnamed end of the primary winding, and means for vibrating said armature.

5. In a device of the kind dmcribed, a pair of terminals adapted to beconnected across a source of current, a transformer having a primarywinding and a secondary winding, means for connecting a point of saidprimary winding to one of said terminals, a vibrating armature adaptedto be vibrated between two extreme positions, a current limiting device,means cooperating with said armature and effective during vibration ofthe armature, for periodically connecting the current limiting devicebetween the other of said pair of terminals and another point of saidprimary winding for a predetermined portion of each cycle of operationof the armature, and means cooperating with the armature and efiectiveduring its operation for short-circuiting the current limiting deviceduring an intermediate part of said portion of each cycle of operationof the armature.

6. In a device of the kind described, a pair of of terminals adapted tobe connected to a source of direct current, a transformer having aprimary winding and a secondary winding, means for connecting a point ofsaid primary winding to one of said terminals, a vibrating armatureadapted to be vibrated between two extreme positions, a current reducingimpedance, means cooperating with said armature and efiective duringvibration of said armature, for connecting said current reducingimpedance between the other of said pair of terminals and another pointof said primary winding for a portion of each cycle of operation of thearmature, and means cooperating with the armature and eflective duringits operation for short-circuiting the current reducing impedance witheach cycle of operation of the armature for an interval of time whichstarts just after the beginning of said portion of each cycle ofoperation of the armature and ends just before the end of said portionof each cycle of operation of the armature.

FRITZ SCHIIGEN.

